There is described in U.S. Pat. No. 4,611,846 such a pick-up head, which comprises a body having a central axis and means for attaching the body to said Z-axis shaft with a central axis of the body coincident with the axis of the shaft. First and second pneumatic piston and cylinder units are arranged in the body in opposed relationship, one on each side of the central axis thereof. First and second jaws, one disposed on each of two opposite sides of the central axis are each connected to, and slidably drivable by, the piston of a respective one of said units, along a path of travel in a direction towards and away from said central axis, each jaw projecting from the body in a direction away from said attachment means.
A brake is provided for retaining one of the jaws in a predetermined position along its path of travel. When an object is to be picked up by the jaws, the pick-up head is lowered by the shaft, to position the object between the jaws, with the brake applied, and the other jaw is moved by its piston and cylinder unit towards the one jaw, to cause the object to be gripped between the jaws. Said one jaw is that jaw which is located in the direction of movement of the shaft, when it is swung to place the object gripped by the jaws in said predetermined position. Said retaining means ensures that said one jaw is not displaced as a result of the rapid translatory movement of the shaft, bearing in mind, that the piston and cylinder units are pneumatic. There is also disclosed in U.S. Pat. No. 4,718,165 a pick-up head for picking up elongate electrical connectors having a contact tail depending therefrom and for placing the connectors on circuit boards to insert the contact tails through holes therein. The pick-up head comprises a frame having a vertical axis and means for attaching the framework to the Z-axis shaft of a pick and place robot with the vertical axis coincident with the axis of the Z-axis shaft. Connector gripping jaws of the pick-up head are operated by the piston and cylinder units connected to one of the jaws for moving the jaws towards and away from one another. The piston and cylinder units are arranged in spaced parallel relationship in the frame.